18 Minutes Of Interval Equals 90 Minutes Of Conventional

Recognise the problem? You want to increase your fitness, but you don't have time to go jogging for 90 minutes three times a week. The solution? We've found it in a study by sports scientists at McMaster University in Canada published in 2006. It shows that an 18-minute interval training session contributes as much to your endurance capacity as a regular endurance training session lasting 90 minutes.

In their article, which was published in the Journal of Physiology, the researchers looked at the effect of interval training and classical endurance training on endurance capacity. The Canadians got eight healthy male students to do endurance training for two weeks, and a similar group to do interval training for two weeks. The students trained three times a week, making sure that there were 1-2 rest days between the sessions.

The table below gives the details of how they trained.

The students in the interval group [SIT group] trained 18-27 minutes each session on an ergometer. During their sessions they cycled 4-6 times as hard as they could for 30 seconds. Between the explosive exertions they cycled for 4 minutes at a moderate speed, during which they could recover. The students in the traditional endurance-training group [ET group] cycled for 90-120 minutes at 65 percent of their VO2max.

At the end of the two weeks, the researchers looked at the amount of time it took the students to expend 180 kcal of energy on the ergometer. The training programme that the interval group had followed reduced the time by 10.1 percent. For the traditional endurance training group the reduction was 7.5 percent. The difference between the groups was not statistically significant.
The researchers extracted a small amount of muscle tissue from their subjects and examined in test tubes how well the muscle cells dealt with lactic acid. They observed that the interval-training programme increased the buffering capacity of the muscle cells by 7.6 percent. For the traditional endurance training group the reduction was 4.2 percent. Once again, the differences between the groups were not significant.

The muscle cells of the subjects in the interval group contained 28 percent more glycogen when at rest. In the other group the amount of glycogen increased by 17 percent – and once again the differences were not statistically significant.

"Two very diverse forms of training induced remarkably similar changes in exercise capacity and selected muscle adaptations that are related to exercise tolerance", the researchers write. "Given the markedly lower training volume in the SIT group, our results suggest that intense interval training is indeed a time-efficient strategy to induce rapid muscle and performance adaptations comparable to traditional endurance training."